Telecommunications and data transmissions have merged into an integrated communication network using technologies such as Voice over Packet (VoP). Many communication networks transmit data using packet protocols, such as the Internet Protocol (IP). VoP uses the existing technology to transmit voice signals by converting the signals into digital data and encapsulating the data for transmission over a packet-based network. Many protocols that VoP uses, however, do not provide a way to identify the sender of packets in certain situations. For example, when an endpoint receives a media packet, the endpoint cannot determine if the packet was sent by a legitimate endpoint or by an illegitimate endpoint. It is generally desirable to determine whether an endpoint is legitimate in certain situations.